Method and apparatus for latent temperature control for a device under test

ABSTRACT

A method and associated algorithm for controlling and optimizing the temperature of a device under test (DUT) through calculation of a moving setpoint which varies from the user-specified DUT core temperature. The method generally comprises (i) calculating a system operating range based on limits imposed by the DUT, associated temperature control system, and thermal conditioning equipment; (ii) determining the allowable operating range for the DUT based on permissible DUT stress and DUT core temperature; and (iii) calculating a control setpoint based on DUT and conditioning system temperature data, one or more pre-selected setup factors, and the system and DUT operating ranges. In another aspect of the invention, variable temperature differential limits are imposed on the CSP as a function of DUT core temperature in order to mitigate thermal shock to the DUT. Methods and apparatus for latent temperature control are also disclosed.

This application is a continuation-in-part of and claims priority toU.S. patent application Ser. No. 09/268,900 filed Mar. 16, 1999 andentitled “Method And Apparatus For Optimizing Environmental TemperatureFor A Device Under Test”, now U.S. Pat. No. 6,449,534, which isincorporated herein by reference in its entirety.

COPYRIGHT

A portion of the disclosure of this patent document contains materialthat is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent files or records, but otherwise reserves all copyrightrights whatsoever.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to temperature control in systems wherein adevice under test (DUT) is thermally conditioned (heated or cooled tosome thermal state) by a thermal conditioning device that adds orremoves heat to/from the device by convection, conduction, or radiation.More particularly, this invention discloses a method and apparatus fordynamically determining an optimum temperature profile for theconditioning device such that the DUT is conditioned as quickly aspossible without exposing either the conditioning device or the DUT tounacceptable temperatures.

2. Description of Related Technology

The nature of heat transfer is such that a differential in temperaturebetween two masses must exist before heat will flow between them. Thegreater the temperature differential, the greater the heat flow will be.This phenomenon operates equally for masses that are separate butadjacent and for masses that are adjacent parts of a monolithic whole.

The rate of transfer of heat within a mass having an internaltemperature differential is regulated by that substance's resistance toheat flow; its thermal conductivity. Every substance exhibits adifferent and predictable thermal conductivity.

It follows that to change the temperature of the center of a mass (the“core”) to some desired temperature, the setpoint, the outside surfaceof the mass (the “skin”) must be exposed to a temperature beyond thedesired core temperature for a time period adequate to allow thesufficient transfer of heat given the mass' thermal conductivity.

The foregoing concept is clearly illustrated by the everyday example ofroasting meat within a conventional oven. The meat is roasted for agiven period of time, as determined by its weight, at a comparativelyhigh oven air temperature in order to achieve a desired lower internalor “core” temperature. The differential temperature causes heat to flowto the core of the meat, thereby raising its temperature.

As previously stated, the transfer of heat into or out of the core of amass consumes a finite amount of time. This time has value, so there isan incentive to achieve the thermal objective (e.g., the desired coretemperature) as quickly as possible. A simple solution to acceleratingthe heat transfer is to increase the temperature differential betweenthe object's skin and it's core. The greater differential will result infaster heat transfer.

However, it will be appreciated that many objects to be heated or cooledhave practical thermal limits that must be respected if the object is tobe not damaged or destroyed by the heating or cooling process. The mostcommon limits that must be considered are the maximum and minimumtemperatures that the skin of the mass can tolerate, and the maximumskin to core temperature differential (thermal stress) that can betolerated.

Therefore, there is a limit to the amount of heat that can be added orremoved from the skin of a DUT during the heating or cooling processwithout exceeding the thermal limits of the object. Controlling thetemperature of the skin of a DUT to that limit will allow the maximumrate of heat transfer to/from the object's core while still respectingthe limits of the object's skin. If there is a thermal differentiallimit as well, then the skin temperature may have to be furtherrestrained to remain within that limit.

Another factor that must be considered is the so-called “latency” of theheating or cooling process. As discussed in greater detail below, if theskin of a DUT is subjected to a more extreme temperature than thatdesired in the object's core until such time as the core achieves thedesired temperature, then the core will be at the desired temperaturebut the skin will be at a more extreme temperature with the mass betweenthe two areas having a temperature gradient therebetween. If no moreheat is added or removed, the entire mass will then equalize intemperature over time. The equalized temperature will be more extremethan the core temperature desired.

Referring again to the example of roasting meat, if a given internal orcore temperature is desired, and the meat is roasted at a highertemperature than the desired core temperature, the oven may be turnedoff when the core temperature has reached a value somewhat less than thedesired value. After the oven is turned off, the core temperature willclimb to the desired value while the skin region transfers the last ofits excess heat to the core in the process of thermal equalization. Itshould be noted, however, that while this approach may be useful inroasting meat where the allowable tolerances are comparatively high, itis not useful in most thermal conditioning applications having morelimited allowable tolerances, and where there is generally littleexperiential basis for the applying the technique.

To change the core temperature of a DUT undergoing conditioning, theskin of the object is typically exposed to a conductive or convectivecontrolled temperature mass that transfers heat to/from the skin. It isthe temperature of this external mass that must be controlled to achievethe desired heat transfer to/from the core of the object. Due to thethermal conductivity and mass of the object there is often substantialthermal latency in the transfer process. One reliable way to achieve thedesired core temperature without “overshooting”, is to regulate theskin's thermal environment such that as the object's core approaches thedesired temperature the object's skin temperature is forced to approachthe same temperature. As the desired temperature is reached, thetemperature difference between the core region and skin regionapproaches zero and heat transfer effectively ceases. See FIG. 1, whichillustrates the response of an exemplary prior art thermal conditioningsystem.

The typical prior art method used for achieving this type of convergentcontrol is to measure the temperature of the thermal environment thatacts upon the object's skin and also measure the temperature of the DUTscore. When determining whether to add or remove heat from the thermalenvironment, it is the average of the two temperatures that is comparedto the temperature objective to make the determination. Thus, theenvironment will be thermally overdriven by the amount the DUTs corevaries from the desired temperature. As the DUTs core approaches thedesired temperature, the average of the two temperatures will requirethat the DUTs environment approach the desired core temperature at thesame rate.

The temperature averaging method described above has the substantialdisadvantage that it has no method for respecting the thermallimitations of the device in which the thermal environment is created,nor does it respect the thermal limits of the DUT being conditioned. Itis quite possible for the averaging method to call for additionalheating/cooling when either the skin of the device being conditioned, orthe conditioning device itself is already at or beyond its limits.Substantial damage to property and risk to operators results from theunrestrained use of such averaging methods.

Therefore, to make effective use of this type of averaging method, it isimperative that the output from the control system that is using theaverage temperature to call for heating or cooling be restrained if thatoutput calls for the addition or removal of heat in a manner that wouldcause the limits of the thermal conditioning device, or the DUT, to beexceeded. If the temperature control system is a simple “on/off”thermostat type control, externally restraining the control systemoutput will be satisfactory. However, if the control method being usedis a more sophisticated method designed around a closed feedback loopthat allows the control system to adapt or modify its control outputbased upon the results of its prior operation, then the externalrestraining of the control outputs can be disastrous.

Almost all precision temperature control systems involve a method thatuses process result feedback in some type of closed loop to adaptivelyregulate temperature while adjusting for the thermal response of theenvironment/device being controlled. Using the feedback data, thecontroller compares the setpoint to the results observed in the feedbackdata in order to increase or decrease the controller's output to betterachieve the setpoint in the process. The feedback loop, and the analysisof the feedback data over time, is the essence of closed looptemperature process control. Feedback data enables the controller todetermine the error in the process control, where error is defined asthe difference between the setpoint and actual process temperature atpoints in time. While there are a multiplicity of control algorithms inuse, all generally rely either on periodic error comparison andintegration or on periodic comparison of feedback data with expectedresults data, or on some combination of these. It is the periodic natureof these routines that allows the controller to adjust the level ofoutput.

It is therefore clear that any system that uses such a control methodwould suffer substantially if its output was externally restrained or“clipped,” since the external clipping of the output would result insubstantial variation to the result of the control system's output. Totolerate this kind of modification of the output signal by an externalsystem, the primary control system would have to be fed accurate data asto the magnitude and timing of the clipping. It is an importantcomponent of all but the most sophisticated of these closed looproutines that the feedback data be reasonably current. That is, thefeedback results most recently obtained are used to adjust the currentcontroller output, thus making the presumption that the control resultseen in that data was related to recent output. Additionally, if thereis substantial latency in the path from controller output to datafeedback, and especially if there are combinations of components withwidely varying thermal time constants within the path that provides thefeedback data, then the controller receiving the feedback data isdeprived of the regular and periodic nature of such data that isrequisite for control. Such latency may occur for example when anassembly of items is stacked on a thermal platform, wherein eachcomponent of the stack provides significant thermal transmissionlatency, and wherein each may have a different thermal latency. Upon thetop of the stack resides the DUT of interest. Another situation wheresuch latency may occur is that of a large mass DUT which is thermallyconditioned by a fluid conditioning system to which the DUT isconnected. Hoses or pipes pass the conditioning medium (e.g., fluid orrefrigerant) which flows between the DUT and the conditioning unit.

Often, it is possible to obtain temperature feedback data from theunderlying platform or thermal conditioning system to control thetemperature of the underlying system. However, such control does notcompensate for heat gains and losses in the path between the DUT and thecontrolled device. Controlling the underlying device can provide astable thermal environment, but seldom will it result in the correct DUTtemperature. On the other hand, if the feedback is obtained from theDUT, the thermal latency of the system will result in over driving ofthe controller outputs that will create an unacceptable controlledtemperature oscillation.

Based on the foregoing, an improved method and apparatus for allowingstable control of a significantly latent DUT at the correct stabletemperature is needed. Such improved method and apparatus would ideallymaintain a stable temperature for the DUT without significanttemperature oscillations or hunting.

SUMMARY OF THE INVENTION

The present invention satisfies the aforementioned needs by providing animproved temperature control method and apparatus useful in the thermalconditioning of devices.

In a first aspect of the invention, an improved method of controllingthe temperature of an object using a temperature control system isdisclosed. The method generally comprises: providing data related to thetemperature of the object; determining the allowable operating range ofthe temperature control system; determining the allowable operatingrange associated with the object based at least in part on the data;calculating a control setpoint based at least in part on the allowableoperating ranges of the temperature control system and the object; andproviding the control setpoint to the temperature control system inorder to control the temperature of the object. In one embodiment, asystem operating range (SOR) and DUT operating range (DOR) arecalculated based on the thermal and stress limits of the DUT,temperature control system (TCS), and thermal conditioning apparatus. Acontrol setpoint (CSP) which is different than the desired DUT coretemperature specified by the user (i.e., the PSP) is then calculatedbased on the difference between the PSP and the secondary temperaturesensing probe input temperature, the value of two predetermined setupparameters, and the relationship between the SOR and DOR, so as toeffectuate varying amounts of heat transfer between the thermalconditioning environment and the DUT. As the desired DUT coretemperature is approached, movement of the control setpoint isterminated and the differential between core and skin temperature of theDUT reduced accordingly until the user-specified setpoint is reached.

In a second aspect of the invention, a device thermally conditionedusing the aforementioned method is disclosed.

In a third aspect of the invention, an algorithm incorporating themethod described above is disclosed. In one exemplary embodiment, thecomputer program is compiled into an object code format which is storedon a magnetic storage medium, and which is capable of being run on adigital computer processor. The algorithm receives inputs (via the hostcomputer system, described below) from instrumentation associated withthe thermal conditioning system, such as chamber/device temperatureprobes, and calculates the Control Setpoint (CSP) which is fed back tothe thermal conditioning system to effectuate control of the chamber anddevice temperature.

In a fourth aspect of the invention, an improved method and algorithmfor controlling the temperature differential limits of a device undertest (DUT) are disclosed. Specifically, variable differential thermallimits are employed as a function of the core temperature of the DUT inorder to control thermal shock to the DUT during various temperaturetransitions.

In a fifth aspect of the invention, a computer system incorporating thecomputer program previously described is disclosed. In one embodiment,the computer system comprises a standard microcomputer (personalcomputer) having a display, magnetic disk drive, microprocessor,internal memory, and input/output port for receiving and transmittingdata to and from the computer. The aforementioned computer program isloaded into the internal memory from the storage area and run by themicroprocessor to effect temperature control of the DUT. In a secondembodiment, a digital processor is integrated with the temperaturecontrol system, the above-described computer program being stored withinthe memory or storage device associated with the processor/TCS.

In a sixth aspect, a thermal conditioning system is disclosed whichincorporates the method, computer program, and computer systempreviously described. In one embodiment, a TCS is operatively coupled toa thermal conditioning chamber having a plurality of temperature probesfor measuring the temperature of the conditioning environment as well asthat of the DUT. The TCS may be of any compatible configurationincluding the PID or fuzzy logic types. The computer system previouslydescribed is operatively coupled to the TCS, whereby the former receivestemperature data and other relevant inputs from the latter, andperiodically calculates and provides a control setpoint (CSP) valuethereto for control of the thermal conditioning chamber.

In a seventh aspect of the invention, an improved method of latenttemperature control of a first object is disclosed. The method generallycomprises: controlling the temperature of a second object which is ableto transfer energy to or from the first object to achieve a firsttemperature; observing at least one event associated with the firstobject after the second object has achieved the first temperature; andsubsequently controlling the temperature of the second object based atleast in part on the at least one event. In one exemplary embodiment,the first object comprises a DUT, and the second object a thermalconditioning device (e.g., thermal platform, oven, or chamber). Thethermal conditioning device is first brought to the desired DUTtemperature, and the DUT subsequently observed (such as via temperatureprobe) to identify both (i) a change in DUT temperature, reflectingresponse to the thermal conditioning device change in temperature; and(ii) stabilization of the DUT temperature. The heating or coolingapplied to the thermal conditioning device is then adjusted based on theobserved difference between the desired DUT temperature and the actualDUT temperature.

In an eighth aspect of the invention, improved thermal conditioningapparatus useful for latent temperature control is disclosed. Theapparatus generally comprises: at least one device for collecting datarelated to temperature of a first object and a second object; and acontroller, operatively coupled to the at least one device and adaptedto control the temperature of the second object, the controlleradjusting the temperature of the second object to a first temperature,and thereafter only after receiving data indicating a substantiallystable temperature of the first object. In one exemplary embodiment, thecontroller comprises an embedded controller having a computer programrunning thereon, the program adapted to implement the latent temperaturecontrol methodology previously described.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating the cyclic temperature response of atypical prior art thermal conditioning system (and DUT beingconditioned) as a function of time.

FIG. 2 is a perspective view of a DUT located within a thermalconditioning chamber (oven).

FIG. 3 is logical flow diagram illustrating the process steps associatedwith one exemplary embodiment of the method of the present invention.

FIGS. 3 a–3 d are logical flow diagrams detailing the individual processsteps of the method of FIG. 3.

FIG. 4 is a graph illustrating the cyclic temperature response of atemperature control system employing the method of the present inventionas compared to that of the prior art system illustrated in FIG. 1 b.

FIGS. 5 a and 5 b are graphs of the temperature of a thermal platformand the corresponding response of an exemplary DUT when conditionedusing variable temperature differential limits during ramp up and rampdown, respectively.

FIG. 6 is a perspective view of a microcomputer system having a computeralgorithm incorporating the method of FIG. 3.

FIG. 7 is a functional block diagram of an exemplary thermalconditioning system incorporating the microcomputer and algorithm ofFIG. 6.

FIG. 8 is a logical flow chart illustrating an exemplary embodiment ofthe generalized latent temperature control methodology of the presentinvention.

FIG. 8 a is a logical flow diagram illustrating specific aspects of themethod of FIG. 8.

FIG. 9 is a functional block diagram of a first embodiment of a latentthermal conditioning system according to the invention.

FIG. 10 is a functional block diagram of a second embodiment of a latentthermal conditioning system according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference is now made to the drawings wherein like numerals refer tolike parts throughout.

As used herein, the terms “thermally condition” and “conditioned” shallrefer broadly to activities wherein one or more DUTs are thermallytreated, evaluated, or otherwise exposed to thermally controlledenvironments for whatever reason, including without limitation thermally“baking” an object according to a time/temperature profile, testing aDUT under varying thermal conditions or extremes, and evaluating themechanical or electrical properties of a DUT.

FIG. 2 illustrates an exemplary thermal conditioning system 100 as usedin conjunction with the invention disclosed herein. Further shown inFIG. 2 is a so-called “device under test” (DUT) 101, which is thermallytested or conditioned by the system 100, having generally an outer or“skin” region 103, and an internal or “core” region (not shown). For thepurposes of this disclosure, the internal temperature of the DUT 101will be referred to as the “core” temperature, and the outside surfacetemperature of the DUT will be referred to as the “skin” temperature.Note that the term “core” does not suggest that that the interior of theDUT be necessarily defined by some required unique core material that isdifferentiated from the surrounding material, although such adifferentiation is none-the-less compatible with the present invention.Likewise, the term “skin” does not suggest that the exterior region orsurface of the DUT is necessarily defined by some required uniquematerial that is differentiated from the substance interior to it.Rather, these terms merely define the relative thermal positions on orwithin the DUT.

For convective environments, such as that existing within the thermalconditioning oven of FIG. 2, the skin 103 is that portion of theexterior region of the DUT that is exposed to the convective fluid whichis typically, but not necessarily, air.

For conductive environments, such as a thermal platform, the skin 103 isthat portion of the exterior region of the DUT that is in contact withthe surface of the thermally conductive mass through which heat is to betransferred to/from the DUT.

For radiant environments, the skin is that portion of the exteriorregion of the DUT which is exposed to the radiation source that is thesource for heat transfer.

Note that while the following discussion relates to convectivetemperature chambers and chamber air temperatures, it will be recognizedthat the same principles generally apply to thermal platforms (and theplatform temperature) as well as radiant heat sources, air forcingsystems and similar devices. Similarly, the following discussion willdescribe the process of heating a DUT, but the concepts apply equallyand simultaneously to cooling a DUT.

The DUT 101 is located within a thermal conditioning chamber (oven) 102of the type well known in the testing and conditioning arts. Primary andsecondary temperature probes 104, 106 are also installed within thechamber 102 to measure environmental temperature and DUT coretemperature, respectively, as described further below. A temperaturecontrol system (TCS) 107 and microcomputer 500 are also operativelyattached to the chamber 102 to provide control of the environment withinthe chamber via the chamber heating and cooling elements (not shown).Additional discussion of the microcomputer 500 and thermal conditioningsystem architecture are presented below with respect to FIGS. 6 and 7,respectively.

The DUT 101 illustrated in FIG. 2 is an integrated circuit, although itwill be appreciated that a large variety of different types of devicesmay be tested and/or conditioned.

Referring now to FIG. 3, an exemplary embodiment of the method ofcontrolling the temperature of a DUT according to the present inventionis illustrated. More specifically, FIG. 3 illustrates a method fordetermining, in a thermal test or conditioning system, an environmenttemperature for a DUT such that the DUT will achieve a specifiedinternal temperature or experience a specified internal temperature rateof change (ramp rate) as quickly as possible without violating thevarious temperature constraints specified by the user. It should benoted that this method is not a control system method such as thoseemployed in prior art “PID loop” or “fuzzy logic” control systems. Suchcontrol systems and their associated algorithms are concerned primarilywith the application of heating and cooling sources to an environment tobest achieve a desired temperature under various conditions. Thosecontrol systems and algorithms are responsible, for example, for turningheaters on and off and for introducing cooling agents such as cryogeniccoolants to the environment to achieve the desired environmenttemperature.

Rather, the method and algorithm of the present invention is designed tosupply information to such control systems to direct the PID loop orfuzzy logic control as to what the environment temperature should be.Because heat transfer only occurs when there is a thermal differentialbetween two bodies, or two parts of the same body, the optimumenvironment temperature is seldom the same as the desired DUTtemperature, especially during thermal transitions of the DUT. Themethod and algorithm described herein defines a method for determiningan effective, and often changing, environment temperature to achieve thedesired thermal results in the DUT.

In the present context, the term “setpoint” is analogous to the term“environment temperature”. The setpoint is that temperature which thetemperature control system (PID loop, etc.) will attempt to maintainwithin the thermal environment. It is also assumed for the purposes ofthis discussion that the proper temperature control system has beenselected for use with the present invention. For example, a SigmaSystems Model C4 temperature control system may be used to effectuatecontrol of the DUT, although it will be appreciated that other types andconfigurations of temperature control system may be used. Theconstruction and operation of such temperature control systems is wellknown in the relevant art, and accordingly will not be discussed furtherherein.

For simplicity of analysis, any latency associated with the chosentemperature control system in achieving the chosen setpoint is assumedto be zero (e.g., it is assumed that the setpoint, the environmenttemperature, and thus the DUT skin temperature, are the same). It willalso be recognized, however, that the skin temperature of the DUT andthe environment temperature must in actuality be different for heattransfer to take place. This difference is not something that is readilytracked or calculated. Hence, the following discussion assumes that thisdifferential temperature does physically exist and is of sufficientmagnitude to effectuate heat transfer from the environment to the skin.

As previously stated, the fundamental concept of the method of thepresent invention is to supply to the temperature control system a“setpoint”, which may change frequently, that is likely different fromthe user-specified (e.g., DUT core) setpoint, and that will: 1) maximizethe speed of the thermal test or conditioning routine; 2) respect thelimits of the DUT with respect to both absolute skin temperature limitsand thermal stress (skin/core differential); 3) respect the thermallimitations of the test or conditioning equipment being used; and 4)maximize the thermal uniformity of the DUT when the user's specifiedsetpoint is reached in the DUT core. As used herein, the user-specifiedsetpoint will be referred to as the Programmed Setpoint or “PSP”, andthe generated setpoint supplied by algorithm to the temperature controlsystem will be referred to as the Control Setpoint or “CSP”.

As described further below, the method and algorithm of the presentinvention will periodically determine that the CSP needs to be changedto meet the objectives of the system. In practice, the algorithminvention recalculates the CSP often and supplies the result of itscalculations to the TCS as a new CSP. For a good part of the thermaltest, especially during periods of thermal transition, the constantlyupdated CSP may be better thought of as a moving setpoint.

Two issues relating to the use of the present invention to supply amoving CSP to the TCS are considered in the design and operation of thepresent invention. First, virtually all temperature control systems relyon a series of feedback data from a closed loop to determine the needfor heating or cooling. The systems use some type of algorithm tocompare the results, over time, of the last output(s) to the feedbackdata, and use that information for current corrective action and toanticipate future requirements so that these requirements can beincluded in the current output as appropriate. The more stable thecontrol environment, the more successful the temperature control systemis likely to be. Therefore, it is desirable that an algorithm supplyinga moving CSP to the TCS do so at a low and constant frequency.

Second, most temperature control systems implement some type of“proportional” or “settling band” (the “P” term of a PID system, forinstance) in which the control system reduces the amount of heating orcooling in a proportional, or proportional-like, manner as the desiredsetpoint is approached. The proportional reduction is further modifiedby the system as it tries to compensate for the effects of thermallosses, thermal latency, etc. and have the controlled environment settleat the desired setpoint. These systems can become very complex in theirmethodology and often substantial effort is needed to create routinesthat will not oscillate unacceptably or show other aberrations as thesetpoint is approached. It is important to recognize therefore that anysystem that supplies the setpoint for such a control routine must notcontribute factors which can cause oscillations or other problems orwhich might, under some circumstances, become sympathetic to and thusamplify existing oscillations.

The present invention addresses both of these issues through (i) theproportional reduction of the CSP/PSP differential as the DUT coretemperature approaches the PSP, and (ii) elimination of the movement ofthe CSP after the PSP is achieved.

For the purposes of this discussion, several additional assumptions aremade. First, it is assumed that at least two temperature sensors (e.g.,primary and secondary probes 104, 106 of FIG. 2) are available. Thesesensors can be of any type capable of returning temperature related datato the controller, as discussed in additional detail with reference toFIG. 7 below. The primary probe is presumed to be within the chamberairstream, and returns a representation of the temperature of thechamber interior environment. The primary probe is the probe used by theTCS to control the temperature of the equipment providing the thermalenvironment for the DUT. The secondary probe can be one probe, or aseries of probes averaged together, that are located inside the DUT,inside a substitute mass of similar thermal characteristics, orotherwise fed representative temperature data. A substitute mass isoften used since many types of DUTs may not permit the insertion of aprobe into their core region without damage to the DUT. Thus, placingthe real DUT in the test or conditioning environment with a thermal“clone” containing the internal secondary probe may be the bestavailable approximation for DUT core temperature data.

Second, it is assumed that the algorithm of the present inventionreceives input from the user and/or thermal conditioning system in theform of the following information:

-   -   1. DUT setpoint (e.g., core temperature desired)    -   2. High & low temperature limits of the system temperature        controller (TCS)    -   3. High & low temperature limits of the temperature equipment        being used (such as a chamber, platform, or other)    -   4. High & low temperature limits of the DUT    -   5. Maximum thermal differential (stress) in degrees allowable in        the DUT at its low temperature limit    -   6. Maximum thermal differential (stress) in degrees allowable in        the DUT at its high temperature limit    -   7. The width, in degrees, of the proportional or settling band        of the temperature control system        Note that all of the information listed above is either readily        calculable, available from the DUT/TCS manufacturer, or        determinable from instrumentation typically associated with the        thermal conditioning system. Accordingly, this information will        not be discussed further herein.

Referring again to FIG. 3, the method 300 of the present invention iscomprised generally of a series of process steps, several of which maybe permuted in order or performed in parallel or series with othersteps. Furthermore, under certain circumstances, not all steps need beperformed, and alternative steps may be substituted for many of thoseshown. Additionally, certain mathematical operations performed as partof the method 300 may be replaced by other operations in order toachieve the same result. For example, the difference between two scalarvalues may be obtained by subtracting the second value from the first,or alternatively subtracting the first from the second and taking theabsolute value or changing the sign of the result. The approach setforth in FIG. 3 is therefore merely illustrative of but one exemplaryembodiment of the method of the present invention.

In simple terms, the method 300 of FIG. 3 moves the CSP beyond (to ahigher temperature, if we are heating the DUT) the PSP by an amountequal to the difference between the PSP and the secondary probetemperature multiplied by a pre-selected first setup parameter (F34).The CSP is then compared to various limits and is further reduced if itexceeds those limits. Specifically, the CSP is compared to the systemoperating range (defined by the aggregation of the high and lowtemperature limits of the DUT, the TCS, and the thermal conditioningequipment). If the CSP is outside the system operating range, then theCSP is reduced sufficiently to be within these limits.

Similarly, the permissible DUT stress is determined by proportioning thehigh and low DUT stress limits based upon a comparison of the secondaryprobe temperature to the DUT range. If the CSP exceeds the combinationof the secondary probe temperature plus the permissible DUT stress, thenthe CSP is reduced such that it is equal to the secondary probetemperature plus the permissible DUT stress at that temperature. This“final” CSP value is then passed to the temperature control system.

Detailed Description of Method and Associated Algorithm

A detailed description of the method 300 of FIG. 3 is now provided withreference to FIGS. 3 a through 3 d, and the definitions and assumptionsprovided herein. While the following discussion is cast in terms of themethod employed within the Applicant's “Intelligent 2 Probe Control”(hereinafter “I2PC”) computer program embodiment, it will be recognizedthat other algorithms, firmware, or even hardware embodiments of thedisclosed method may be used with equal success. It is also noted thatwhile the terms “determine” and “calculate” are used in describing thefollowing method, these terms are not meant to be limited to specificprocesses. For example, it is contemplated that in lieu of calculating aspecific value, such value may be provided by the DUT or TCSmanufacturer, or otherwise obtained without the need for explicitcalculation.

In the first process step 302 (FIG. 3 a), an allowable or SystemOperating Range (SOR) is determined for the temperature control system.This process step 302 is comprised of several sub-steps 304, 306, 308,as follows. In sub-step 304, a system lower aggregate operating limit(LAOL) is determined as being the higher of the following: (a) the lowlimit of the system temperature controller; (b) the low limit of thetemperature equipment; or (c) the low limit of the DUT. Similarly, insub-step 306, a system upper aggregate operating limit (UAOL) isdetermined to be the lower of: (a) the high limit of the systemtemperature controller; (b) the high limit of the temperature equipment;or (c) the high limit of the DUT. Finally, in sub-step 308, the systemoperating range (SOR) is defined as the range between and including theLAOL and the UAOL determined in sub-steps 304 and 306.

Note that in the present embodiment, a valid SOR is defined as one wherethe LAOL is a lower temperature than the UAOL. If this condition is notmet, the algorithm exits with and generates an appropriate error code.

Next, in the second process step 310 (FIG. 3 b), the allowable or DUToperating range (DOR) is determined by calculating the DUT permissiblestress at the current secondary probe temperature. In the first sub-step312 of the second process step 310, the DUT low limit permissible stressis subtracted from the DUT high limit permissible stress to determinethe DUT stress range. In sub-step 314, the DUT low limit temperature issubtracted from the DUT high limit temperature to determine the DUTrange in degrees. Next, the secondary probe temperature is subtractedfrom the DUT high limit temperature in sub-step 316. The percentage ofthe DUT temperature range represented by the secondary probe temperatureis then calculated in sub-step 318 by dividing the result of sub-step316 by the result of sub-step 314. The DUT currently permissible stress(DCPS) is determined at the current secondary probe temperature (e.g.,that of the DUT core) by multiplying the result of sub-step 312 by theresult of sub-step 318 and subtracting this product from the high limitpermissible stress for the DUT in sub-step 319.

Next, the DUT upper operating limit (DUOL) is calculated by adding theDCPS to the current secondary probe temperature (DUT core) in sub-step320. Similarly, the DUT lower operating limit (DLOL) is determined bysubtracting the DCPS from the current secondary probe temperature insub-step 322. Finally, in sub-step 324, the DOR is defined as thetemperature range between and including the DUOL and the DLOL.

In the third process step 326 (FIG. 3 c), the system parameters areevaluated to determine if the I2PC algorithm can operate to generate avalid CSP. It should be noted that in the present embodiment, someportion of the DOR must overlap a portion of the SOR in order for thelimits of all devices to be respected. If the core temperature of theDUT plus or minus the permissible stress at that temperature defines arange (e.g., the DOR) that is outside the range that is defined by theSOR (e.g., the limits of the DUT, equipment, and temperature controlsystem) then it will not be possible to determine a setpoint that iswithin both ranges and thus which respects the limits of both the DUTpermissible stress and those associated with the remainder of thetemperature control system.

Referring again to FIG. 3 c, the DUOL and DLOL are each compared to theUAOL and LAOL in sub-steps 328 a, 328 b and sub-steps 329 a, 329 b,respectively, of process step 326. If either: (I) the DUOL is less thanthe UAOL and greater than the LAOL; or (ii) the DLOL is greater than theLAOL and less than the UAOL, then a valid CSP may be calculated by thealgorithm. If neither of these conditions are met, then an error code isgenerated by the algorithm. It will be appreciated that while a parallelapproach to these comparisons is illustrated in FIG. 3 c, other methodsof comparison and logical relationships may be substituted.

In the fourth process step 330 of the method 300 (FIG. 3 d), the ControlSetpoint (CSP) is calculated. Initially, the secondary probe value issubtracted from the PSP, and the absolute value of this quantity takenin sub-step 332. In sub-step 334, the aforementioned absolute value ismultiplied by a first setup factor (F34). See Appendix A. In step 336,the value of a second setup factor (F35) is added or subtracted asappropriate to the result. The first setup factor acts as a scalingfactor or multiplier for the proportional term of the CSP, while thesecond factor represents a thermal overdrive value (in degrees). In thepresent embodiment, the first and second setup parameters are numericalvalues pre-selected or input by the operator, although it can beappreciated that these parameters can be supplied dynamically during thetemperature conditioning process from another algorithm or source ifdesired. Typical values for the first setup factor F34 are in the rangeof 0.0 to 5.0 (default value=2). Typical values for the second setupfactor are −20.0 to +20.0° C. (default=5.0° C.), or −36.0 to +36.0° F.(default 9° F.). The foregoing values are merely illustrative; othervalues may be chosen.

In sub-steps 338 and 339, the result of sub-step 336 is compared to zeroand if greater than zero, is added to the PSP to determine the so-called“unlimited” CSP. Next, the result of sub-step 339 is compared to theUAOL and the DUOL in sub-step 340. The CSP is set to the lesser of thesethree values (e.g., unlimited CSP, UAOL, and DUOL). Lastly, the resultof sub-step 340 above is compared to the LAOL and the DLOL per sub-step342. The CSP is then set to the greater of these three values. This isthe “final” CSP.

In the final process step 344 of the method 300 of FIG. 3, the “final”CSP is passed to the temperature control system for use thereby.

It will further be recognized that the method 300 (and associatedalgorithm) disclosed herein has several operational attributes whichprovide advantages over prior art systems and methods. Specifically, thealgorithm of the present invention (i) automatically reduces the excessheating/cooling as the DUT core approaches the PSP; and (ii)automatically stops moving the setpoint and enters into normal PIDcontrol when either the PSP is reached (within the tolerance of thesettling band temperature tolerance parameter F31, described below), orwhen a predetermined period of time without significant change in theDUT core temperature expires. These attributes are discussed inadditional detail below.

Automatic Reduction of Excess Heating/Cooling—Because the CSP exceedsthe PSP by an amount related to the difference between the secondaryprobe and the PSP, the amount the CSP leads the PSP is automaticallyreduced as the DUT core temperature approaches the PSP. Using the CSP tocause the thermal environment to exceed the PSP results in fasterthermal transfer to/from the DUT to the increased differential. Assumingthat the DUT skin temperature approaches the environment temperature,the DUT core is the primary beneficiary of the increased heat transfer.

As the DUT core continues to increase in temperature due to thisincreased differential, the secondary probe temperature (DUT core)begins to approach the PSP. As this occurs, the difference between thePSP and the secondary probe temperature becomes smaller and the CSP isaccordingly reduced. All of this will occur with a continuous reductionin the CSP lead of the PSP and thus the environment temperature suchthat the DUT skin temperature will be reduced as the core temperature isrising. The result is that the skin and core temperatures nearlycoincide as the setpoint is reached. The setup parameter F35 allows theoperator to account for thermal latency inherent in the DUT, which isrelated to the heat capacity of the DUT material(s) as well as thethermal conductivity of the material between the DUT skin and coreregion.

Automatic Termination of Setpoint Movement—Sub-steps 336 and 338described above reduce or enlarge the amount of lead of the CSP over thePSP by the amount of the second setup parameter F35 so that when theCSP/PSP difference equals or is less than the magnitude of the setupparameter, the PSP and the CSP are the same value. From this point on inthe temperature transition, the system will behave as a one probe systemrelying on the primary probe in the airstream of the exemplary chamberdescribed herein. When the PSP is reached by the secondary probe, plusor minus the value of the settling band parameter F31, the I2PCalgorithm is exited in favor of normal PID control. Thus, when used inconjunction with the present invention, the temperature control systemdoes not have to arbitrate or compensate for a moving setpoint whiletrying to settle on the user's defined setpoint while inside thesettling band.

Additionally, the I2PC algorithm is exited in event that the PSP(+/−F31) is not reached by the secondary probe within a predeterminedperiod of time (i.e., “times out”). This condition is utilized topreclude the algorithm from operating indefinitely in the case where thePSP can not practically be achieved, such as where the maximum rate ofheat generation within a test platform is not sufficiently high tooffset radiated heat or other losses from the DUT, or where calibrationerrors within the temperature probes or other equipment exist. In oneembodiment, the I2PC algorithm calculates the change in secondary probetemperature over time; if secondary probe temperature does not vary by apredetermined amount within a given period of time, I2PC will be exited.It will be recognized that other “time out” schemes may be used, such asmeasuring the time from entry of the last user-specified setpoint, ortime from achieving a certain percentage of the desired setpointtemperature. Furthermore, while the aforementioned time out function ishard coded into the firmware of the apparatus of the present invention,it will be appreciated that other methods may be used, such as by timeout parameters input by the user via software.

The foregoing approach allows a very aggressive thermal overdriving ofthe system (e.g., environment temperature greater than the DUT coretemperature and the PSP) to achieve a desired temperature within a highlatency DUT. However, to allow stable PID control, once the DUT hasreached or passed through the PSP +/−F31, discontinuing I2PC adjustmentsallows normal PID control to continue without the risk of interferenceby the I2PC algorithm. Note that the I2PC algorithm is reinstated witheach new setpoint specified by the user. When a new setpoint isspecified, the algorithm of the present invention recognizes (1) that anew setpoint has been entered, and (2) the ramp required (i.e., whetherthe ramp is UP or DOWN), so it knows which way to adjust the CSP.

It should also be noted that the approach of the present inventionallows stable and predictable operation of the temperature controlsystem as a whole. Specifically, since the CSP is calculated by the I2PCalgorithm on each “loop” of the feedback processing within the TCS (orat another regular interval specified by the operator), a regularvariation of CSP results. As previously discussed, the operation of theTCS (and any associated PID or fuzzy logic device) is generally enhancedwhen corrections are applied in such a periodic fashion.

FIG. 4 illustrates the cyclic temperature response of an exemplarytemperature control system employing the method of the presentinvention, as compared to that of the prior art system illustrated inFIG. 1 a. As illustrated in FIG. 4, the I2PC algorithm of the presentinvention achieves a much more rapid change in DUT core temperature thanthe prior art system, due primarily to the use of thermal overdrive inthe present invention. Note that the prior art system does not usethermal overdrive, but rather ramps the environmental (e.g., chamber orplatform) temperature up or down to the PSP, which results in a muchlower temperature differential between the environment and the DUT core,and thereby slows the response time of the system. In a cyclic testingscenario where one or more DUTs must be tested or conditioned over manythermal cycles, the time savings and economies afforded by the presentinvention are substantial. Additionally, as previously noted, thealgorithm of the present invention respects the critical thermaldifferential limits associated with the thermal conditioning system, itscontroller, and the DUT itself while accomplishing this result.

Appendix A illustrates one embodiment of the aforementioned algorithmaccording to the present invention.

Description of Variable Differential Limits

Referring now to FIGS. 5 a and 5 b, an improved method and algorithm forcontrolling the temperature differential limits of a device under test(DUT) is described. As shown in FIGS. 5 a and 5 b, the differentialtemperature existing between the thermal environment (in the presentexample, a thermal chamber) and the DUT core temperature varies as afunction of the DUT core temperature. This approach is utilized based onthe physical property of many DUTs that the maximum allowabledifferential temperature within the DUT varies as a function of thetemperature of the DUT. This property results largely from thermallyinduced stresses occurring within the materials of the DUT which maydamage or impair the DUT if the aforementioned differential temperaturelimitations are exceeded (i.e., thermal “shock”). For example, at 0° F.,a given DUT may be able to sustain a differential temperature of ΔT₁° F.without excessive thermal stress, whereas at 100° F., the maximumallowable differential is ΔT_(u)° F. In the exemplary ramp-up of FIG. 5a, the allowable temperature differential at low temperature issignificantly larger than that at high temperature, thereby indicatingthat the DUT under test is more restricted in heatup/cooldown rate athigher temperatures. In the present embodiment, the allowable lower andupper temperature differentials are calculated based on the absolutelower and upper temperature limits of the DUT; that is, the allowabletemperature differentials ΔT₁ and ΔT_(u) at the absolute lower and uppertemperature limits for the DUT (DOR from step 310 above) are used asendpoints to “envelope” the entire temperature range. This approach isconsidered conservative with respect to all allowable temperaturedifferentials between the upper and lower absolute temperature limits.While linear extrapolation between these endpoints is used in thepresent embodiment, it will be appreciated that other functionalrelationships (f(T) in Eqn. 1 above) may be used as well. Note that incontrast to step 310 of the previously described method, in which theabsolute temperature limits of the DUT (and thus the DOR) aredetermined, the specification of variable differential temperaturelimits seeks to restrain or control the difference between the DUT coreand the conditioning environment temperature (e.g., air temperature inthe conditioning chamber). The aforementioned variation in allowabletemperature differential is preferably accomplished using an algorithmwhich periodically samples the DUT core temperature (per input receivedfrom the secondary probe) and calculates the allowable differential forthat temperature based on the user's initial input of (i) lower andupper allowable differential temperatures ΔT₁ and ΔT_(u) and (ii) thefunction f (T). This calculated limit is then imposed upon the systemvia the CSP, which is adjusted so as to maintain the differential withinthe prescribed limit.

Description of Computer System and Thermal Conditioning System

FIG. 6 illustrates one exemplary embodiment of the algorithm of thepresent invention as installed on a microcomputer system 500. As shownin FIG. 6, the microcomputer system 500 comprises a display 502, inputdevice 503, non-volatile storage device (e.g., magnetic disk drive) 504,and output port 506. Additionally, the system includes a centralprocessor 509 and internal memory 510 (see FIG. 7). The aforementionedtemperature control algorithm in the form of a computer program (I2PC)rendered in object code is stored ideally on the disk drive 504 (or adiscrete storage medium such as a floppy disk 520 associated therewith),or loaded into the internal memory of the computer system 500, where itmay be recalled by the processor and associated peripherals such as aDMA module for execution. The output port 506 is coupled to thetemperature control system 107 of FIG. 2, the latter receiving the CSPfrom the algorithm/processor in the form of data transmitted via theoutput port 506 and associated data connection, such as a serial port,IEEE-488 (General Purpose Instrument Bus), or Ethernet connection. Whilethe temperature control algorithm in the present embodiment resideswithin the storage devices of the microcomputer system 500, all or partof the algorithm may also reside within temperature controller of theassociated thermal conditioning device (e.g., temperature chamber,thermal platform, thermal chuck, or thermal airstream), or othernon-volatile programmable storage device such as an EEPROM which isassociated with the temperature control system.

Referring now to FIG. 7, an exemplary thermal conditioning systemarchitecture utilizing the microcomputer system of FIG. 6 is described.As illustrated in FIG. 7, the conditioning system 100 comprises themicrocomputer system 500 with algorithm (not shown), a temperaturecontrol system 107, a thermal conditioning chamber 102, primary andsecondary temperature probes 104, 106, and data interface 604. Aspreviously noted, the temperature sensors 104, 106 may be of any type oftemperature sensor which generate data related to the temperature of theenvironment or component being measured, such as a resistancetemperature detector (RTD) or thermocouple. The thermal conditioningsystem 100 of the present invention utilizes two 500 ohm platinum RTDprobes, although others may be used as well.

During operation, temperature data obtained from the probes 104, 106 aswell as that generated by the TCS 107 is passed to the microcomputer 500and algorithm wherein the CSP is periodically calculated by thealgorithm and passed via the data interface 604 back to the TCS. It willbe appreciated by one of ordinary skill in the relevant arts thatnumerous alternate configurations incorporating hardware, software,and/or firmware may be may be employed in practicing the inventiondisclosed herein. For example, a thermal platform could be substitutedfor the conditioning chamber 102 of FIG. 7. Similarly, an algorithmincorporating the method of the present invention could be stored withinthe internal memory of a digital signal processor located within the TCS107, or within a remote networked computer, as opposed to using themicrocomputer system 500 of FIG. 7.

Latent Temperature Control Methodology and Apparatus

In another aspect of the invention, an improved apparatus and method forlatent temperature control is now described in detail. It will berecognized that while the invention is described in terms of anexemplary algorithm or computer program adapted to run on an embeddeddigital processor, the methodologies described herein may be readilyadapted to other hardware and software environments by those of ordinaryskill.

In its simplest form, the algorithm of the present invention controlsthe temperature of the underlying device, such as a thermal platform, orfluid conditioning system, to affect the temperature of a DUT so as toachieve a temperature specified as the DUT setpoint. Notably, thepresent invention is advantageously made “event triggered”; i.e., itadjusts the output of the controller based on the occurrence of events(e.g., stabilization of DUT temperature or some other observable orgroup of observables) rather than solely relying on a constantlychanging error or differential signal. This is particularly advantageousin applications where there is a high degree of latency due to, forexample, the DUT thermal characteristics, or the physical configurationof the conditioning apparatus (e.g., a significant run of piping betweenthe thermal controller and the conditioning chamber or platform).

It will also be appreciated, however, that the use of the latent controlmethodology of present invention is not restricted to homogeneousapplications, but rather may be used alone or in a heterogenous controlsystem (i.e., one with both latent control and prior art PID or feedbackloop features). For example, outputs from a conventional PID/feedbackcontroller and the latent controller of the present invention may beused as inputs to control logic or algorithms which determine theappropriate control signal(s) based on the multiple inputs, oralternatively which use one signal as a gating or enabling/disablingsignal. Similarly, the temperature control methodologies previouslydescribed herein with respect to FIGS. 1–7 may be used in conjunctionwith the latent control techniques of the present invention. Myriadcombinations employing the latent approach may be fashioned by one ofordinary skill given the disclosure provided herein.

FIGS. 8 and 8 a illustrates one exemplary embodiment of the latenttemperature control methodology according to the invention. In thisembodiment, the temperature controller (see FIGS. 9 and 10 below)directly controls the temperature of the underlying conditioning deviceusing feedback from a first temperature sensor (i.e. Probe 1, or P1)located in, or on, such device. The controller uses a second temperaturesensor (i.e. Probe 2, or P2) to measure the temperature of the DUT. Thecontroller's outputs affect directly only the temperature of theunderlying conditioning device, while indirectly affecting thetemperature of the DUT according to latency present between theconditioning device and DUT.

When the controller receives a new DUT setpoint value (step 802), acontrol setpoint value (control_(—)setpoint) is set equal to this newDUT_(—)setpoint per step 804. The controller adjusts its output, basedupon data from P1, to obtain and then maintain the control setpointtemperature in the underlying conditioning device (step 806). When theunderlying device is thermally stable, the controller continues tocontrol it at the control setpoint temperature while monitoring thetemperature of the DUT as reported by inputs from P2 (step 820 of FIG. 8a). When the temperature of P2 has changed (step 822), as measured byeither (i) expiration of a predetermined interval (F46) by theDUT_(—)change_(—)timer (which was started upon the conditioning devicetemperature achieving the control setpoint) (step 824 a); or (ii) theDUT temperature as measured by P2 has changed by a predetermined amount(e.g., F45) (step 824 b), the stability of the DUT temperature is thenevaluated over subsequent periods (step 826). The foregoing “change”criterion is used to affirm that the DUT has in fact responded to theinitial temperature stimulus before stabilization (i.e., mitigates thepossibility that the controller will identify pre-stimulus stability aspost-stimulus stability). DUT thermal stability is determined accordingto a predetermined stabilization criterion (i.e., the “event” of thepresent embodiment) per step 808. Specifically, in the presentembodiment, either (i) the DUT temperature band and time at temperatureparameters (F40, F41) are used; i.e., if P2 maintains within the bandfor a predetermined time, then stability is achieved (step 828 a); or(ii) the DUT_(—)stability_(—)timer has reached a prescribed timeoutvalue (F43) (step 828 b). Once stability is achieved (step 830), thedifference between the DUT temperature (as reported by P2) andDUT_(—)setpoint triggers the subsequent modification of the controlsetpoint per step 810. In the illustrated embodiment, the temperatureband stabilization of step 808 is accomplished by differencing of two ormore temperature measurements of the DUT over a finite period of time(F41), and the comparison of the absolute value of this difference to apredetermined threshold band parameter (F40).

Alternatively, however, other stabilization criterion may be used aloneor in conjunction with the foregoing. For example, a rate criterion maybe generated, such as in the case where a change in DUT temperature(positive or negative) of 1 degree F. occurs over a period of τ=10seconds, with the resulting rate of change ( 1/10=0.1° F./sec) beingthen compared to a predetermined rate criterion (say, for example, 0.2°F./sec) to determine if stabilization has occurred. It will berecognized that literally any manner or form of stabilization methodand/or criterion may be used consistent with the invention, whetherbased on P2 temperature or some other indicia.

In terms of the subsequent modification of the control setpoint per step810, this is accomplished in the illustrated embodiment by firstdetermining an average temperature parameter (e.g., P2_(—)average_(—)temp) during a given averaging interval (F42). Next, thetemperature conditioning device setpoint is adjusted by an amountrelated to the difference between the current control setpoint and P2_(—)average_(—)temp. The underlying device is then brought to the newcontrol setpoint temperature (step 806), and the process 800 is repeated

If the P2 temperature remains stable at the DUT setpoint, the process800 is finished except to maintain the status quo. However, thecontroller constantly monitors the DUT temperature at P2 so that if apreviously stable DUT changes temperature, the adjustment can be madefor these changing conditions in the same manner as prior adjustments.

Appendix B hereto provides an algorithmic illustration of the foregoingexemplary embodiment of the latent control process of the invention.

In another embodiment of the method 800, the initial control setpoint ismade to vary from the DUT_(—)setpoint by either a fixed amount(“offset”), or by an amount determined by a relationship (deterministicor otherwise) based upon for example experiential/historical data oruser-specified data. Likewise, subsequent adjustments to the controlsetpoint may be modified by similar data.

It is further noted that the exemplary embodiment of the process 800(and apparatus of FIGS. 9 and 10 below) includes timer functions in allprocesses that can halt the main control process 800 if certainconditions are not met, so that the algorithm will not “hang” 800 forextended periods in the event that decision data are unavailable orinsufficient to satisfy the decision criteria. However, it will beappreciated that the invention may be practiced without such timerfunctions if desired.

If the DUT is known to have or requires room for thermal oscillation orchange, then either a tolerance for these excursions, or a system suchas windowed averaging of P2 over time, may be included to allow thecontrol system to differentiate between such excursions and unwanted, orunexpected, thermal changes.

Additionally, it will be recognized that other types of “events” (i.e.,other than those previously described, and/or other than those based onthermal stabilization) may also be used alone or in conjunction with theaforementioned approach. For example, the occurrence of a particularartifact in the DUT or underlying device thermal profile (such as a flatspot or cusp, or minima/maxima in first or second derivative curves) mayindicate the need for alteration of the control setting. Alternatively,the occurrence of a non-thermal event (e.g., a change in electricalconductivity, capacitance, mechanical property such as stress or strain,etc.) in the DUT may be used as the basis for latent control accordingto the invention.

In yet another embodiment, the system controller is programmed withalgorithms for adjusting the temperature of the underlying conditioningdevice based on the properties (e.g., non-linearities) of specificmaterials. For example, if it is known that within a certain temperaturerange, greater or smaller increments of temperature changes in theunderlying device causes greater or smaller changes in the DUTs stabletemperature respectively, then such information can be stored in thecontroller (such as in a look-up table or other profile) and accessed topermit on-the-fly adjustment of the algorithm 800 under such conditions.This approach advantageously allows the controller to bring the DUT tothe desired temperature more quickly than use of non-material specificprofiles.

In yet another embodiment, the controller is adapted to receive dataregarding the DUT's initial temperature before setting the initialcontrol_(—)setpoint parameter. Thus, if the DUT's initial temperaturesignificantly differs from the DUT_(—)setpoint, the initial Controllersetpoint may be set at a value that will converge the DUT setpoint andDUT temperature (P2) more quickly. For example, selective and controlleduse of temperature overshoot (i.e., setting the platform or otherconditioning device setpoint temperature higher than the DUT_(—)setpointvalue for a period of time) may be employed.

In yet another embodiment, the controller is programmed to bring the DUTto a series of DUT_(—)setpoint values over time. For example, afterbringing the DUT to a first setpoint, and then maintaining it at thesetpoint for a given period of time, the controller then brings the DUTto a second setpoint which may be higher or lower than (or bear somedeterministic relationship to) the first setpoint. This processcontinues until all the programmed or deterministic setpoints are met.

Referring now to FIGS. 9 and 10, exemplary embodiments of temperatureconditioning apparatus according to the present invention are described.As shown in FIG. 9, a first embodiment of the apparatus 900 comprises anassembly of components 904 a–f stacked on a thermal platform 902,wherein each component of the stack provides significant thermaltransmission latency, and wherein each may have a different thermallatency. A controller 907 comprising an embedded temperature controllerof the type well known in the temperature controller arts and having thealgorithm 800 previously described running thereon (via program or flashmemory), and thermal conditioning medium 909, are coupled to theplatform 902 so as to provide temperature control of the platform 902.At the top of the stack resides the DUT (Device Under Test) 906 ofinterest. Temperature probes P1 and P2 provide temperature inputs to thecontroller 907 from the platform 902 and DUT, respectively. The thermalconditioning medium 909 may comprise, for example a refrigerant (e.g.,R12 or R114) or liquefied nitrogen or helium in the vapor phase, aliquid phase heat transfer medium, or other medium. Ancillary mechanismsfor maintaining the proper state and distributing/returning theconditioning medium 909 as appropriate are also provided, such as forexample a compressor and TXV (thermostatic expansion valve) in the caseof the aforementioned refrigerant(s). The design and construction ofsuch thermal conditioning devices are well known in the art, andaccordingly not described in greater detail herein.

Another exemplary embodiment of the latent temperature control apparatusis shown in FIG. 10, where latency may occur as a result of significantDUT mass and/or significant length of hoses or piping runs 1006, such aswhen the thermal “engine” (e.g., chiller or thermal fluid conditioningsystem) 1004 and the controller 1007 are physically disparate from theDUT 1002.

It will also be appreciated that the methodology of the presentinvention may be readily adapted to a temperature chamber apparatus withassociated air circulation/forced-air system (including associated ductsand hoses).

It will be recognized that while certain aspects of the invention aredescribed in terms of a specific sequence of steps of a method, thesedescriptions are only illustrative of the broader methods of theinvention, and may be modified as required by the particularapplication. Certain steps may be rendered unnecessary or optional undercertain circumstances. Additionally, certain steps or functionality maybe added to the disclosed embodiments, or the order of performance oftwo or more steps permuted. All such variations are considered to beencompassed within the invention disclosed and claimed herein.

While the above detailed description has shown, described, and pointedout novel features of the invention as applied to various embodiments,it will be understood that various omissions, substitutions, and changesin the form and details of the device or process illustrated may be madeby those skilled in the art without departing from the invention. Theforegoing description is of the best mode presently contemplated ofcarrying out the invention. This description is in no way meant to belimiting, but rather should be taken as illustrative of the generalprinciples of the invention. The scope of the invention should bedetermined with reference to the claims.

1. Temperature control apparatus, comprising: a conditioning deviceadapted to generate a range of temperatures; a first temperature probeadapted to generate first signals related to the temperature of a DUT; asecond temperature probe adapted to generate second signals related tothe temperature of at least a portion of said conditioning device; acontroller, operatively coupled to said conditioning device and saidprobes and having an algorithm associated therewith, said algorithmbeing adapted to control the temperature of said conditioning devicebased at least in part on said first and second signals; wherein saidcontroller is further adapted to control the temperature of saidconditioning device by: (i) establishing a first temperature for saidconditioning device; (ii) identifying at least one change in said DUTthereafter; (iii) identifying at least one stabilization event in saidDUT thereafter; and (iv) adjusting the temperature of said conditioningdevice based at least in part on said first and second signals and saidacts of identifying.
 2. The temperature control apparatus of claim 1,wherein said adjusting the temperature of said conditioning devicefurther comprises maintaining for at least a period of time a targettemperature of said conditioning device.
 3. The temperature controlapparatus of claim 1, wherein at least one of said acts of identifyingcomprises identifying a change or event based on a parameter other thantemperature.
 4. The temperature control apparatus of claim 3, whereinsaid parameter comprises DUT electrical conductivity.
 5. The temperaturecontrol apparatus of claim 3, wherein said parameter comprises DUTcapacitance.
 6. The temperature control apparatus of claim 3, whereinsaid parameter comprises DUT frequency response.
 7. The temperaturecontrol apparatus of claim 3, wherein said parameter comprises amechanical property associated with said DUT.
 8. Temperature controlapparatus, comprising: a conditioning device adapted to generate a rangeof temperatures; a first temperature probe adapted to determine thetemperature of a first object; a second temperature probe adapted todetermine the temperature of at least a portion of said conditioningdevice; a controller having an algorithm associated therewith, saidalgorithm being adapted to control the temperature of said conditioningdevice based at least in part on said temperatures of said first objectand said at least said portion of said conditioning device; wherein saidcontroller is further adapted to control the temperature of saidconditioning device by: (i) achieving a first temperature for saidconditioning device; (ii) identifying at least one change in said firstobject thereafter; (iii) identifying at least one stabilization event insaid first object thereafter; and (iv) adjusting the temperature of saidconditioning device based at least in part on said temperatures of saidfirst object and said at least said portion of said conditioning deviceand said acts of identifying.
 9. Temperature control apparatus,comprising: a conditioning device having means to generate a range oftemperatures; a first temperature probe with means for generating firstsignals related to the temperature of a DUT; a second temperature probewith means for generating second signals related to the temperature ofat least a portion of said conditioning device; a controller,operatively coupled to said conditioning device and said probes andhaving an algorithm associated therewith, said algorithm having meansfor controlling the temperature of said conditioning device based atleast in part on said first and second signals; wherein said controlleris further adapted to control the temperature of said conditioningdevice by: (i) establishing a first temperature for said conditioningdevice; (ii) identifying at least one change in said DUT thereafter;(iii) identifying at least one stabilization event in said DUTthereafter; and (iv) adjusting the temperature of said conditioningdevice based at least in part on said first and second signals and saidacts of identifying.
 10. The temperature control apparatus of claim 8,wherein said adjusting the temperature of said conditioning devicefurther comprises maintaining for at least a period of time a targettemperature of said conditioning device.
 11. The temperature controlapparatus of claim 8, wherein at least one of said acts of identifyingcomprises identifying a change or event based on a parameter other thantemperature.
 12. The temperature control apparatus of claim 11, whereinsaid parameter comprises the electrical conductivity of said firstobject.
 13. The temperature control apparatus of claim 11, wherein saidparameter comprises capacitance of said first object.
 14. Thetemperature control apparatus of claim 11, wherein said parametercomprises frequency response of said first object.
 15. The temperaturecontrol apparatus of claim 11, wherein said parameter comprises amechanical property associated with said first object.
 16. Thetemperature control apparatus of claim 9, wherein said adjusting thetemperature of said conditioning device further comprises maintainingfor at least a period of time a target temperature of said conditioningdevice.
 17. The temperature control apparatus of claim 9, wherein atleast one of said acts of identifying comprises identifying a change orevent based on a parameter other than temperature.
 18. The temperaturecontrol apparatus of claim 17, wherein said parameter comprises DUTelectrical conductivity.
 19. The temperature control apparatus of claim17, wherein said parameter comprises DUT capacitance.
 20. Thetemperature control apparatus of claim 17, wherein said parametercomprises DUT frequency response.
 21. The temperature control apparatusof claim 17, wherein said parameter comprises a mechanical propertyassociated with said DUT.
 22. Temperature control apparatus, comprising:a conditioning device adapted to generate a range of temperatures; afirst temperature sensor adapted to generate first signals related tothe temperature of an object; a second temperature sensor adapted togenerate second signals related to the temperature of at least a portionof said conditioning device; a controller, operatively coupled to saidconditioning device and being adapted to control the temperature of saidconditioning device based at least in part on said first and secondsignals; wherein said controller is further adapted to control thetemperature of said conditioning device by: establishing a firsttemperature for said conditioning device; identifying at least onechange in said object thereafter; identifying at least one stabilizationevent in said object thereafter; and adjusting the temperature of saidconditioning device based at least in part on said first and secondsignals and said acts of identifying.
 23. The temperature controlapparatus of claim 22, wherein said adjusting the temperature of saidconditioning device further comprises maintaining for at least a periodof time a target temperature of said conditioning device.
 24. Thetemperature control apparatus of claim 22, wherein at least one of saidacts of identifying comprises identifying a change or event based on aparameter other than temperature.
 25. The temperature control apparatusof claim 24, wherein said parameter comprises object electricalconductivity.
 26. The temperature control apparatus of claim 24, whereinsaid parameter comprises object capacitance.
 27. The temperature controlapparatus of claim 24, wherein said parameter comprises object frequencyresponse.
 28. The temperature control apparatus of claim 24, whereinsaid parameter comprises a mechanical property associated with saidobject.